The proposed research will continue an analysis of the neural mechanisms through which ovarian hormones control the expression of specific estrous behaviors in female hamsters and cats. In female golden hamsters, effects of estrogen or progesterone on the responses to lordosis-controlling somatic stimuli of midbrain, especially deep tectal, single neurons will be examined. Single unit activity will be recorded in anesthetized as well as unanesthetized, freely behaving hamsters. In female cats, effects of estrogen on the caudolateral medullary control of the estrous cry response to genital stimulation will be assessed by single-unit recording in acutely-prepared animals. The results of these investigations should reveal mechanisms through which ovarian hormones alter the activity of specific brain stem neuronal systems in order to affect behavioral responsiveness to sensory stimuli which normally occur during mating.